Francis turbines and centrifugal pumps



March 1965 R. s. SPROULE ETAL 3,174,719

FRANCIS TURBINES AND CENTRIFUGAL PUMPS Filed June 12, 1962 2Sheets-Sheet l INVENTORS ROBERT 5. PE'OLJLE LAM/BEING. M. BOYD March 23,1965 R. s. SPROULE ETAL 3,174,719

FRANCIS TURBINES AND CENTRIFUGAL PUMPS Filed June 12, 1962 2Sheets-Sheet 2 F'EOM CASING xal 7 g 22 31 I3 36 o g 35 FEOM CASNGINVENTORS. ROBERT S. SPEOU LE LAM/$1}: NCE M. BOYD United States Patent3,174,719 FRANCIS TURBINES AND (IENTRIFUGAL PUMPS Robert S. Sproule,Montreal, Quebec, and Lawrence M.

Boyd, Senneville, Quebec, Canada, assignors to Dominion EngineeringWorks Limited Filed June 12, 1962, Ser. No. 201,881 3 Claims. (Cl.25326) This application is a continuation-in-part of our applicationSerial No. 120,301 filed June 28, 1961, now abandoned.

This invention relates to new and useful improvements in rotary fluidmachines, whereby losses due to fluid friction are reduced. This isaccomplished by the introduction of an additional fluid of less densityand absolute viscosity than the working fluid, into the spacessurrounding the runner or impeller shrouds.

In hydraulic turbines, significantly improved efliciencies may bederived from reduction of fluid friction, the extent of suchimprovements being dependent on the operating hydraulic head and beingprogressively greater with increasing head. An improvement of 1%efiiciency, capitalized, could amount to as much as the price of theturbine.

The factors which atfect fluid friction are: The hydrauliccharacteristics of the working fluid, wetted area and velocity.

The general equation for friction loss is of the form F =K.n.d Ffriction horsepower K=a parameter n=the revolutions per minute of themachine d=the diameter of contact between the rotating parts and theworking fluid.

Numerous attempts have been made to increase the efliciency of rotatingfluid machines by reduction of fluid friction. These attempts have beenbased on the concept of reducing either K or d, or a combination of bothof these factors, but the maximum possible benefits obtain able havenever been realized.

The present invention relates to increasing the efliciency of rotaryfluid machines by the optimum combination of the lowest value ofeifective parameter (K), for specified design conditions, and minimumdiameter of contact between the rotating parts and the working fluid.

The value of K decreases directly with decrease of absolute viscosity ofthe fluid between the relatively rotating parts. Therefore, by replacingthe working fluid which is normally in contact with the outer surface ofthe rotating parts, by a fluid of less absolute viscosity, considerableimprovements in efficiency can be realized.

Although this invention is applicable to turbines, pumps andpump-turbines, the following disclosure will, for the sake of clarity,be referred specifically to hydraulic turbines of the Francis type.

As an example, air is a fluid of less absolute viscosity than water,hence, within the field of hydraulic turbines, attempts have been madeto increase the efiiciency of Francis turbines by replacing with air thewater which is ordinarily between the stationary and rotating parts. Awell known method has been to seal the runner band and crown at theirperipheries, leaving the inner portions of the spaces between the crownand the stationary turbine parts, and between the band and thestationary turbine parts, open to the draft tube. Air is then introducedto these spaces so that leakage water can pass to the draft tube withoutaccumulating in the spaces mentioned above.

In the case of Francis turbines designed for high head operation, thediameter of the runner at the inflow is ice considerably greater thanthe diameter at the out-flow. Since the fluid friction losses at arunner seal vary as the 4th power of the diameter, it is desirable tokeep the seal diameter to the minimum practicable value. This is to saythat the seal for the lower shroud of such a vertical Francis turbineaccording to this invention, is located at the lower extremity of theshroud, Where the diameter is minimum. The crown seal could actually beatfected on the runner shaft diameter, but this, although giving theminimum possible seal diameter would give rise to very high downwardhydraulic thrust on the runner, with an increment of thrust bearing loadwhich would in most cases be undesirable, if not intolerable. It isevident that the thrust increment due to employment of the minimum crownseal diameter would result in greater friction losses in the thrustbearing; this increase of thrust bearing losses could otiset thereduction of friction losses in the crown seal.

In the preferred execution of this invention, the crown seal diameter isintermediate between the outside diameter of the upper shroud and thediameter of the runner shaft, whereby the optimum compromise is affectedand the minimum aggregate thrust bearing and seal losses is achieved.

Referring to the drawings:

FIG. 1 is a fragmentary sectional view embodying one execution of thepresent invention, as applied to a high head Francis turbine;

FIG. 2 is an enlarged partial sectional view taken on line 22 of FIG. 1,looking in the direction of the arrows;

FIG. 3 is a fragmentary sectional view showing the preferred executionof the present invention, as applied to a high head Francis turbine,shown opposite hand from FIG. 1.

In the drawings the invention has been shown by way of illustration asapplied to a high head Francis turbine, but it is understood that itcould be equally well applied to other types of rotary fluid machines.

Referring to the drawings wherein similar reference characters designatecorresponding parts throughout, and more particularly to FIG. 3, theFrancis turbine shown embodying the invention includes upper runnershroud 1 and lower shroud 2, connecting the runner blades 3 to eachother and to shaft 4. Water under pressure is supplied to the runner atdistributor 5 containing the conventional Wicket gates and isdischarged, at much lower pressure, to the draft tube at 6. Seals, showngenerally at 7 and 8, are of the type described in our co-pendingapplication Serial No. 808,546 dated March 26, 1959, now Patent No.3,081,975, suitably modified as described in the following, althoughthey may be any type of conventional space seal embodying theaforementioned modifications. Pipes 30 and 31 supply a relatively smallflow of air to spaces 11 and 10 respectively.

To fully describe the operation of this invention, consider the turbineas starting from rest and running up to normal operational speed.

With the turbine at rest, spaces 10 and 11 are filled with water. As therunner commences to rotate, it imparts rotary motion to this waterthereby subjecting it to centrifugal force. Introduction of air, whichis a fluid of less density than water, to space 11 creates a void in thewater by centrifugal action and, as the ratio by volume of air to waterincreases, the void extends progressively from the lower end 32, to theupper end 33, of the outside of the lower shroud 2. The water which hasbeen displaced by the air escapes through clearance 14, whereupon itjoins the main stream of water entering the runner. This is not to saythat all water is expelled from space 11. Such water as remains hasrotary motion imparted to it by the rotating body of air, acted upon bythe lower shroud 2, and tends to climb the sloping wall 34. I

In the same way, introduction of air to space creates a void in thewater by centrifugal action and, as the ratio by volume of air to waterincreases, the void extends progressively from the inner zone 35, to theouter zone 36, of the outside of the upper runner shroud 1. The waterwhich has been displaced by the air escapes through clearance 13,whereupon it joins the main stream of water entering the runner. Again,not all water is expelled from space 10, and the remaining water hasrotary motion imparted to it by the rotating body of air, acted upon bythe upper runner shroud 1, and tends to run down the sloping wall 37,also any water which makes contact with the outside of upper shroud 1between inner zone 35 and outer zone 36, will be expelled centrifugallythrough clearance 13.

In the event that air is supplied to spaces 18 and 11 in excess of thatnecessary to maintain a balanced condition, the excess air will escapethrough clearances 13 and 14 and so automatically maintain a balancedcondition. Any excess air which escapes will be of such a small amountthat it will have no adverse affects on the operation of the turbine.

Conventional space seals are not effective enough to retain the air inspaces 10 and '11; water is therefore fed to space seals 7 and 8 at apressure higher than the air pressure. This water can normally be takenfrom any convenient source, for example, the penstock, by way of pipes17 and 18 to seals 8 and 7 respectively. Leakage across sections 19 and20 of seals 7 and 8 respectively is small, due to the small pressurediiferential across these sections. Sections 21 and 22 of seals 8 and 7respectively are subjected to substantially the full pressure dropacross the turbine between the distributor and draft tube and the amountof this leakage is approximately the same as that through a conventionalturbine.

The small amount of leakage water from seal sections 19 and 25) passesinto spaces 10 and 11 respectively, and is subjected to the same actionsas those imparted to the water originally in these spaces, as describedabove. This is a continuous and stable operation.

Leakage from seal sections 21 and 22 passes through the turbine into thedraft tube in a conventional manner.

From the foregoing it will be seen that we have provided new andimproved means for obtaining all of the objectives and advantages of theinvention.

We claim:

1. In a hydraulic turbine, a runner and a housing, said runnercomprising an upper shroud provided with a sealing shoulder on its upperface, a plurality of blades and a lower shroud, a radial runner inletbounded by said shrouds in the region of their similar maximumdiameters, an axial runner discharge through said lower shroud in theregion of its minimum diameter, the peripheral edges of said shroudsbeing positioned in cooperating relationship to corresponding bores insaid housing dimensioned so as to provide running clearances betweensaid peripheral edges and said bores, a lower seal cooperating with saidlower shroud near to said minimum diameter, a stationary element of saidlower seal associated with said housing, an upper seal cooperating withsaid sealing shoulder, a stationary element of said upper sealassociated with said housing, said upper seal diameter beingsubstantially less than the diameter of said peripheral edges, a lowerannular space bounded by said lower seal, said housing, and said lowershroud, an upper annular space bounded by said upper seal, said housing,and said upper shroud outside of said sealing shoulder, means forintroducing sealing water into each of said seals intermediate of itsaxial extremities, and means for introducing air into each of saidannular spaces whereby centrifugal separation of air and water iseffective in expulsion of water from said annular spaces by way of saidrunning clearances.

2. A hydraulic turbine as claimed in claim 1 in which the upper sealdiameter and the lower seal diameter are substantially the same. 3. .Ina hydraulic turbine having a runner with axially spaced upper and lowershrouds to define a radial flow duct therebetween, each of said shroudshaving a large diameter intake edge and a small diameter discharge edge,a housing about said runner having a distributor for dischargingpressure liquid directly into the radial flow duct of the runner, saiddistributor having a close running clearance with the large diameterintake edges of the shrouds, said housing having upper and lower wallsextending radially inwardly toward the axis of the runner but spacedtherefrom so as to define therebetween annular chambers having smoothlycontinuous wall portions, labyrinthseal means interposed between thesmall diameter discharge edges of the shrouds and the adjacent upper andlower walls of said housing for preventing the escape of high pressureair into the low pressure end of the flow duct, conduit means providingcommunication between the supply of pressure liquid to the runner andthe labyrinth seal means whereby the pressure liquid lubricates thelabyrinth seal means, and means for supplying pressurized air to saidannular chambers at a higher pressure than that of the pressure liquidin the distributor whereby, upon rotation of said runner, liquid isexpelled from said annular chambers and is prevented from re-enteringsaid annular chambers, the sole means for escape of the pressurized airbeing through the clearance spaces between the large diameter intakeedges of the shroud and the distributor.

References Cited by the Examiner UNITED STATES PATENTS 1,823,702 9/31Ring 253-117 1,934,628 ll/33 Powell 253-417 1,962,380 6/34 Briggs253-117 3,051,441 8/62 Sproule 253-117 FOREIGN PATENTS 179,275 8/54Austria. 184,880 3/56 Austria. 714,290 11/41 Germany.

KARL I. ALBRECHT, Primary Examiner.

WALTER BERLOWITZ, JOSEPH H. BRANSON, 112.,

Examiners.

1. IN A HYDRAULIC TURBINE, A RUNNER AND A HOUSING, SAID RUNNERCOMPRISING AN UPPER SHROUD PROVIDED WITH A SEALING SHOULDER ON ITS UPPERFACE, A PLURALITY OF BLADES AND A LOWER SHROUD, A RADIAL RUNNER INLETBOUNDED BY SAID SHROUDS IN THE REGIONS OF THEIR SIMILAR MAXIMUMDIAMETERS, AN AXIAL RUNNER DISCHARGE THROUGH SAID LOWER SHROUD IN THEREGION OF ITS MINIMUM DIAMETER, THE PERIPHERAL EDGES OF SAID SHROUDSBEING POSITIONED IN COOPERATING RELATIONSHIP TO CORRESPONDING BORES INSAID HOUSING DIMENSIONED SO AS TO PROVIDE RUNNING CLEARANCES BETWEN SAIDPERIPHERAL EDGES AND SAID BORES, A LOWER SEAL COOPERATING WITH SAIDLOWER SHROUD NEAR TO SAID MINIMUM DIAMETER, A STATIONARY ELEMENT OF SAIDLOWER SEAL ASSOCIATED WITH SAID HOUSING, AN UPPER SEAL COOPERATING WITHSAID SEALING SHOULDER, A STATIONARY ELEMENT OF SAID UPPER SEALASSOCIATED WITH SAID HOUSING, SAID UPPER SEAL DIAMETER BEINGSUBSTANTIALLY LESS THAN THE DIAMETER OF SAID PERIPERHAL EDGES, A LOWERANNULAR SPACE BOUNDED BY SAID LOWER SEAL, SAID HOUSING, AND SAID LOWERSHROUD, AN UPPER ANNULAR SPACE BOUNDED BY SAID UPPER SEAL, SAID HOUSINGAND SAID UPPER SHROUD OUTSIDE OF SAID SEALING SHOULDER, MEANS FORINTRODUCING SEALING WATER INTO EACH OF SAID SEALS INTERMEDIATE OF ITSAXIAL EXTREMITIES, AND MEANS FOR INTRODUCING AIR INTO EACH OF SAIDANNULAR SPACES WHEREBY CENTRIFUGAL SEPARATION OF AIR AND WATER ISEFFECTIVE IN EXPULSION OF WATER FROM SAID ANNULAR SPACES BY WAY OF SAIDRUNNING CLEARANCES.